Recently for widening use of an organic electroluminescence device (in the present specification also referred to as organic EL device), materials using phosphorescent compounds with high luminous efficiency have been eagerly developed.
In general, an organic EL device comprises one layer or two or more layers of organic layer sandwiched between an anode and a cathode. Using a polymer as a material for forming these layers, a film can be easily formed by coating a solution wherein this polymer is dissolved, and enlargement of the area and production on a larger scale of the device become possible.
For example, Patent document 1 discloses an organic EL device having a layer comprising a polymer with structural units derived from a hole-transporting carbazole derivative and an electron-transporting oxadiazole derivative, and a phosphorescent compound.
In the case wherein the polymer contains structural units derived from the carbazole derivative, however, there have been problems that high luminous efficiency cannot be attained and that the durability of the element is low.
To overcome these problems, Patent document 2 tried using a triphenylamine derivative instead of the carbazole derivative as a hole transport compound. Specifically this literature discloses a polymer having structural units derived from a triphenylamine derivative, an oxadiazole derivative and a phosphorescent compound.
However, in some combinations of monomers employed, distribution of the structural unit derived from each compound became heterogeneous in the polymer due to difference in polymerizability of each compound. With an organic EL device using a polymer with such heterogeneous distribution, there have been problems that the luminous efficiency is not high and that the durability of the element is also low.
For these reasons, it has been desired to develop materials that are suitable for enlargement of the area and scale-up of production and also provides high luminous efficiency and high durability.
[Patent document 1] JP-A-2002-363227
[Patent document 2] JP-A-2005-97589